Membranes can be used for various purposes in irrigation drip emitters in connection to waterways formed in the emitter. For example, a membrane may be used for controlling the flow rate of water discharged by the emitter, for sealing between parts of the emitter, for defining valves in the emitter and/or for defining flow-paths within the emitter.
In control of flow rate, for example, the membrane operates to control liquid flow out of the emitter so that it is substantially independent of pressure at an inlet of the emitter for a range of pressures typically encountered in irrigation applications. For this purpose, the membrane is normally located between inlet and outlet waterways of the emitter and in response to increase in pressure of the entering water undergoes distortion that operates to increase resistance to liquid flow through and out of the emitter.
When used, in another example, for defining flow path waterways by e.g. sealing between parts of the emitter, the membrane may be pressed between body members of the emitter and/or be fitted to overlie waterway grooves in one or more body members of the emitter; in order to define waterway flow paths through the emitter by e.g. sealing areas of the emitter against egress of liquid.
Optimal design and/or shape of membranes for drip emitters may thus differ depending on the purpose for which it is used in the emitter. For example, a membrane used for flow rate control, may require certain specific elastic properties while for defining flow paths in the emitter additional and/or other considerations may be applicable.
U.S. Pat. No. 4,210,287 discloses an emitter unit provided with a resiliently flexible membrane, which is releasably retained within a body member so as to serve a double function. On the one hand, whilst being exposed to the irrigation flow pressure in the conduit to serve in exercising differential pressure control, and, on the other hand, to define, with respect to a flow restricting waterway groove formed in the body member, a flow-restricting waterway flow-path.